PROJECT SUMMARY The long-term goal of this project is to understand the ability of the proteins S100A5 and S100A6 to bind to and recognize their target proteins. S100A5 and S100A6 are small proteins that bind to downstream target proteins in the cell in response to calcium; however, the precise targets remain poorly understood. S100A5 and S100A6 are both upregulated in disease states, including various cancers and heart disease; however, not knowing their binding partners hampers efforts to understand the causes or consequences of this effect. The first goal of the project is to identify possible binding targets using ?phage display,? an approach for identifying short protein fragments that may bind to the protein. This approach, while powerful, is also plagued by false positive rates. To get around this, the project is guided by the words of a famous geneticist: ?nothing in biology makes sense except in light of evolution.? This means that averaging phage display/binding results from the human proteins versus other animals amplifies the signal of biologically important protein fragments. The second goal is to identify the pieces on S100A5 and S100A6 that are important for its interactions with its possible targets. Revealing the evolutionary path by which a protein acquired its current protein targets efficiently reveals the residues responsible and thus sets up mechanistic studies of its binding.